The present invention relates to an apparatus for detecting deflection of the spin axis of a gimbal supported spinning mass relative to the gimbal axis. The apparatus is suitable for use in gyroscopic instruments and is particularly intended for use in inertial navigation systems such as are found in missiles, aircraft, satellites and other steered devices.
Gimbal supported spinning mass gyroscopes are commonly used in inertial navigation systems for maintaining a fixed orientation in space or tracking a predetermined path. Thus a gyroscope is commonly deployed in missile guidance systems for terminal homing. The gyroscope comprises a spinning magnet rotatably mounted on inner and outer gimbals for azimuthal and elevational displacement of the spin axis. Thus any deflection of the spin axis will normally have two components, azimuth and elevation, and a suitable detector arrangement must be provided to detect the two components of deflection. Control signals corresponding to deflections of the spin axis are used in the missile guidance system which controls the orientation of the missile. The detected signals must therefore be very accurate for correct terminal homing.
In the past an induction coil method has been used to measure the angle of the spinning magnet. This method is subject to excessive fluctuations, nonlinearity, and other inaccuracies which significantly limit the angle resolution. Better angle resolution than can be produced with this method is desirable for accurate compensation of the gyroscope drift and for correct terminal homing.
Various optical systems for detecting spin axis deviations of gimbal rotors in gyroscopic instruments have been devised in the past. Such systems involve light reflectors for reflecting light incident on the rotor onto suitable detectors for providing an indication of spin axis deviations. These systems are typically relatively complex and require special mounting assemblies in the gimbal housing.
One such system is shown in U.S. Pat. No. 3,422,686 of Unruh, where deviations of a gimbal rotor spin axis are detected by reflecting light off a mirrored surface in the system through various reflective surfaces and apertures onto photo detectors. The optical system is relatively complex and is arranged such that when the spin axis of the rotor is correctly aligned, an annular image is traced on the detector which is concentric with a circular aperture through which light is reflected onto the detector.
In U.S. Pat. No. 3,499,332 of Fingerett, et al. a gyroscope having a spherical rotor is provided with four light sensors supported on the inner gimbal surrounding a light source. A mirrored surface on the rotor reflects light onto the sensors which respond to X and Y axis deviations of the rotor axis.
In U.S. Pat. No. 4,361,760 of Rodgers the gimbal rotor of a gyroscope is provided with a special reflective non-reflective pattern to reflect light onto two fiber optic sensors mounted concentrically on the outer gimbal shaft.